Surfactant Monomers Research Articles

Morphology of surfactant mixtures at solid/liquid interfaces: High-speed AFM observation

We characterized time-dependent morphological changes in cationic monomeric/gemini surfactant mixtures adsorbed on silica using high-speed atomic force microscopy (HS-AFM). The gemini surfactant employed in this study was 1,2-bis(dodecyldimethylammonio)ethane dibromide (12-2-12). This surfactant was mixed with a monomeric surfactant, hexadecyltrimethylammonium bromide (HTAB), in the presence of a background electrolyte. The HS-AFM measurements revealed that wormlike surface aggregates that formed in an HTAB solution transformed into a bilayer within a few hundred seconds after the HTAB solution was replaced by an HTAB + 12-2-12 mixed solution. This morphological change was reversed within a few hundred seconds after this solution was replaced by the initial HTAB solution. These time-dependent morphological changes were supported by simultaneous quartz crystal microbalance with dissipation monitoring (QCM-D) and ellipsometry measurements. The energy dissipation, monitored by QCM-D, changed reversibly in response to the solution exchanges.

A Thermodynamic Micellization and Hemolysis Evaluation of Polysorbate Surfactants in Combination with Short-Chain Alcohols

Surface active agents have been used in many pharmaceutical formulations for different purposes as penetration enhancers. In this study, the penetration enhancement activity of four nonionic surfactants from polyoxyethylene sorbitan fatty acid esters alone and in combination with some short-chain alcohols on red blood cells were investigated. Hemolysis at different concentrations of each nonionic surfactant (0.1, 0.2, 0.5, 1, and 2%) and ethanol, isopropyl alcohol, glycerol, and propylene glycol (0.5, 1, 2, 5, and 10% w/v) were investigated. Critical micelle concentration (CMC) and micellization thermodynamic parameters of tween 80 in presence of ethanol and glycerol at different concentrations were determined. The influence of the ethanol and glycerol on nonionic surfactant micelle formation was evaluated by determining CMC and micellization thermodynamic parameters of tween80 at different concentrations of alcohol-tween mixtures. The mixture of Tween 20 and glycerol have the lowest hemolytic activity while tween 80-ethanol mixture has the highest hemolysis activity. The self-aggregation of surfactant monomers was affected by short-chain alcohols. The structure breaking ability of alcohol and their interactions with the hydrophilic-hydrophobic groups of surfactants might be the main factors for changing the micelle formation. The CMCs of tween 80 was incremented by increasing the concentration of alcohol. The results indicated that by adding and increasing short chain alcohols the CMCs increased also the CMCs were increasing through raising the temperature (while in the presents of surfactants alone the CMCs decreased by raising temperature).

Preparation of a Gemini Surfactant from Mixed Fatty Acid and its Use in Cosmetics

Abstract Among the surfactants, dimeric surfactants represent a niche group with multifunctional properties. In this work a modified gemini surfactant was synthesized using symmetrical fatty acids. Due to the spacers used to combine the two symmetrical monomers, the synthesized gemini surfactant is cationic. The structure of the compound was confirmed with 1H-NMR. The most advantageous property of the gemini surfactant is that it has a lower surface tension, i. e. less than 35 mNm–1 at 25°C, compared to monomeric surfactants. The surface tension was determined with a Kyowa tensiometer. The CMC (critical micelle formation concentration) was calculated according to the pyrene method and detected by UV spectroscopy at 25°C. The very low CMC is another market advantage of the gemini surfactant. Hydrophobicity and hydrophilicity of the synthesized compound were checked by the emulsification method. The ability of the synthesized gemini surfactant to wet and foam and the emulsification index at different pH values were tested. Based on the results, the gemini surfactant was used in formulations for hair and skin care. Conditioners and creams were prepared with the synthesized compound and the properties were analyzed at different concentrations of the gemini surfactant in the respective formulation.

Regression-BPNN modelling of surfactant concentration effects in electroless Ni[sbnd]B coating and optimization using genetic algorithm

Critical micelle concentration (CMC) is an important factor to avoid the formation of micelles from monomeric surfactant molecules. Trisodium citrate stabilized electroless NiB (ENi-B) coating on aluminium alloy (Al7075-T6) is attempted with the addition of amphoteric surfactant, 3-(N, N-Dimethylmyristylammonio) propanesulfonate (3-DMAPS), to enhance the surface finish (Ra) of the coatings. The main aim of the study is to investigate the influence of surfactant concentration on average surface roughness in ENi-B bath and determine the CMC of 3-DMAPS at minimum Ra. Mathematical models relating the concentration of amphoteric surfactant (0–0.162 g/L) as an independent variable and Ra as a dependent variable are developed using univariate regression analysis (Linear, quadratic, power, and exponential models) and back propagation neural network (BPNN) algorithm. The coefficient of determination (R2) is used to evaluate the goodness of fit between the models, and the BPNN model is found to be the best fit (R2 > 0.98). The minimum Ra of 0.171 ± 0.001 μm was achieved at the CMC of 0.049 g/L (0.135 mM) from the genetic algorithm (GA) using the validated models developed by quadratic regression analysis and BPNN as fitness functions. SEM, XRD and AFM techniques were carried out for the characterization of ENi-B coatings with and without surfactant at CMC.

Synthesis of dimeric surfactant based on neem fatty acid and its characterization

A new cationic dimeric surfactant (DS) has been synthesized using fatty acids separated from neem oil. The dimeric surfactant synthesized from neem oil-based fatty acid holds antibacterial property like the neem oil. A well plate method was used for the assay. Prepared dimeric surfactant was characterized by FTIR and 1H NMR, while fatty acids were characterized by GC, acid value, and SAP value. The most effective CMC (critical micellar concentration) value and surface properties of the dimeric surfactant were characterized by the pyrene probe method as well as the Wilhelmy method. Surface tension (SFT) and interfacial tension (IFT) value helps to know the wide application of the compound. Dimeric surfactant generally shows lower surface tension as compared to monomeric surfactants. Neem fatty acid-based dimeric surfactant shows 28 mN/m surface tension. Lamella strength is also good for the compound whereas interfacial tension was 3 mN/m. Such an effective surfactant was also used in nanoemulsion and particle size was determined, and it gives stable emulsion from the emulsification index. Dimeric surfactant prepared from neem fatty acid shows very good wettability and foaming property.

Spacer length effect on the aggregation behaviours of gemini surfactants in EAN

As the symbol of gemini surfactants, the spacer group connects two surfactant monomers and plays an important role in the self-assembling of gemini surfactants. Recent attention has been paid to the effects of spacer nature and length in aqueous systems. In this study, the aggregation behaviours of quaternary ammonium gemini surfactants 12-s-12 with different spacer length (s = 2, 3, 4, 5, 6, 8, 10, 12) have been investigated in the protic ionic liquid EAN. The micellization behaviour was characterized by surface tension measurement. With the help of small-angle X-ray scattering (SAXS), the size and shape of aggregates were verified. The spacer length effect could be reflected by the changes in the micellization and phase behaviours of 12-s-12/EAN systems. The critical packing parameter of gemini molecules would decrease monotonically with the spacer length, which is supported by SAXS results. Due to the charge screening effect of EAN, the aggregation behaviours of 12-s-12 would be mainly influenced by spacer length. Our results would be the important supplement to the spacer length effect of gemini surfactants in the nonaqueous systems. With the increase of spacer chain length, the reverse hexagonal lyotropic liquid crystal phase would transform into the micellar phase.

Thermodynamically stable structure of hydroxy alkane sulfonate surfactant monomers in water achieving high water solubility and a low CMC.

Although sodium internal olefin sulfonates (IOSs) derived from petrochemicals are known to act as anionic surfactants, these compounds have few practical applications and their interfacial properties have not been examined in detail because they have complex compositions and are challenging to prepare. However, IOSs obtained from vegetable oils have recently been applied to detergents. The present work represents the first study of the IOS sodium 5-hydroxyhexadecane-4-sulfonate (C16-4S-5OH) as a pure substance. The properties of C16-4S-5OH in aqueous solution were assessed by differential scanning calorimetry, equilibrium surface tension measurements, Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy. This compound was found to have a low Krafft point and a low CMC, both of which are necessary for a modern sustainable surfactant. Although these two characteristics are normally difficult to achieve simultaneously, this work demonstrated that C16-4S-5OH in aqueous solution has a highly fixed stereostructure that enables both properties to be achieved. The C16 main carbon chain of this compound acts as a C12 and a C4 chain both oriented in the same direction, while the hydrophilic sulfo and hydroxy head groups form a rigid cyclic moiety including two carbons of the C16 alkyl chain based on hydrogen bonding. This highly fixed molecular structure of the C16-4S-5OH in water is maintained in the monomer and micellar states below and above the CMC, respectively.

Spectroscopically Quantifying the Influence of Salts on Nonionic Surfactant Chemical Potentials and Micelle Formation.

The influence of two salts (NaSCN and Na2SO4) on the micellization of a nonionic surfactant (1,2-hexanediol) is quantified using Raman multivariate curve resolution spectroscopy, combined with a generalized theoretical analysis of the corresponding chemical potential changes. Although the SCN- and SO42- anions are on opposite ends of the Hofmeister series, they are both found to lower the critical micelle concentration. Our combined spectroscopic and theoretical analysis traces these observations to the fact that in both salt solutions the ions have a greater affinity for (or are less strongly expelled from) the hydration shell of the micelle than the free surfactant monomer, as quantified using the corresponding chemical potentials and Wyman-Tanford coefficients. This probe-free experimental and theoretical analysis strategy may readily be extended to micelle formation processes involving other surfactants, salts, and cosolvents, as well as to other sorts of aggregation and binding processes.

Relationship between the Bulk and Surface Basicity of Aliphatic Amines: A Quantum Chemical Approach.

To assess the surface basicity constant (pKb) of aliphatic amine films, the use of a theoretical approach recently developed to evaluate the pKa of carboxylic acid monolayers on the water surface is tested. The present paper gives a new full picture of the change of acid–base properties of surfactants during their aggregation at the air/water interface. The exploited approach is simple because it does not involve the construction of thermodynamic cycles but uses the Gibbs energies of the formation and dimerization of surfactant monomers in neutral and ionized forms in the aqueous and gaseous phases. The quantum chemical semiempirical PM3 method is applied to perform calculations using a conductor-like screening model, which takes into account the aqueous phase. The calculation shows that aliphatic amines, as well as carboxylic acids, are characterized by a change of the value of the basicity/acidity constant during the film formation. The film formation of surfactants leads to a decrease in their acid–base properties, i.e., the surface pKa values of carboxylic acids and pKb values of amines increase. However, unlike carboxylic acids, there is practically no dependence of the surface pKb value on the alkyl chain length of the aliphatic amine, which is caused by almost identical contributions of one CH2 fragment to the solvation Gibbs energy of neutral and ionized monomers within the calculation error. The obtained results agree with existing experimental data.

Investigation of surface adsorption and thermodynamic properties of 1-tetradecyl-3-methylimidazolium bromide in the absence and presence of tetrabutylammonium bromide in aqueous medium

The aggregation behavior of imidazolium-based long-chain ionic liquid 1-tetradecyl-3-methylimidazolium bromide [C14mim][Br] has been investigated in the absence and presence of (1, 2, and 5) mM tetrabutylammonium bromide (C4H9)4NBr at three temperatures (298.15, 308.15, and 318.15) K. The critical micelle concentration (CMC), surface parameters such as maximum surface excess concentration (), the minimum area surfactant monomer at the air/water interface (), surface tension at CMC () and surface pressure () are determined by employing conductivity and surface tension measurements. Various thermodynamic parameters of micellization such as standard free energy of micellization (), standard enthalpy of micellization (), and standard entropy of micellization () are calculated by utilizing the temperature dependence of CMC observed using conductivity study. Other thermodynamic parameters such as free energy of adsorption (Δ) and surface free energy () are also evaluated. Refractive index measurements and UV–vis spectroscopic studies have been utilized to confirm the values of CMC obtained via conductivity and surface tension measurements. FTIR spectroscopic studies signify the various interactions prevailing in the system constituting long-chain ionic liquid and electrolyte.

Mechanistic study to investigate the injection of surfactant assisted smart water in carbonate rocks for enhanced oil recovery: An experimental approach

More than half of the world's discovered oil is held in carbonate reservoirs, most of which are naturally oil-wet fractured reservoirs. Oil Recovery efficiency can be improved noticeably if the rock wettability is changed from an oil-wet to a water-wet state. However, what factors control the wettability alteration are not clearly specified. In this study, a comprehensive mechanistic study is performed using different experimental tools to investigate the effects of active ions, non-active ions, CTAB, and different combinations of ions and CTAB on the sample rock's wettability. The results indicate that using CTAB and a smart water solution, in which the sodium and chloride ions are eliminated and the concentration of sulfate ions is increased, (SW-0NaCl-4SO42− + 1CTAB) reduced the contact angle to 43.58°. The zeta potential value of the oil-wet calcite powder increased from −61.12 to −7.6 mV after treatment with SW-0NaCl-4SO42− + 1CTAB. Moreover, the mean roughness value of oil-wet calcite powder increased from 5.02 to 25.89 nm after treatment with SW-0NaCl-4SO42− + 1CTAB. In fact, sulfate ions are capable of removing the strongly adsorbed carboxylic groups from the surface and changing the wettability of the calcite surface to a more water-wet state. Also, the cationic surfactant monomers tend to ionically react with carboxylic groups and separate them from the calcite surface. Moreover, the removal of sodium and chloride ions also leads to significant changes in the wettability. The imbibition results showed that the change of wettability from an oil-wet to a more water-wet state results in a critical increase in oil recovery efficiency during imbibition of distilled water into the calcite rock slice. High oil recovery efficiency can be obtained by optimizing the smart water solution composition and using a proper concentration of surfactant.

Synthesis and evaluation of a hyperbranched copolymer as viscosity reducer for offshore heavy oil

As is well known, resin and asphaltene greatly increase the viscosity of the oil, which causes difficulty for heavy oil to flow and to be displaced. Therefore, reducing the viscosity of heavy oil effectively is the key to enhance oil recovery. A hyperbranched copolymer named as HVR grafted with hydrophilic surfactant monomers, was synthesized and evaluated in this paper as an alternative to reduce the offshore heavy oil viscosity. The synthesis method of HVR through free-radical copolymerizing using the third generation polyamidoamine dendrimer, acrylamide, acrylic acid and surfactant monomers in deionized water was detailed in this paper. Thereupon the characterization of HVR were described by Fourier transform infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy. The physical properties of HVR solution including apparent viscosity, oil viscosity reducing ability, interfacial tension were comprehensively studied. Otherwise the effect of HVR on sheet structure of asphaltene aggregate and asphaltene aggregation inhibition-dispersion activity were measured by X-ray diffraction and ultraviolet–visible spectrophotometer, respectively. The results indicate that apparent viscosities of HVR solution is relatively not high. For example, after shearing with a Waring blender at 3500 rpm for 20 s, the viscosity of 2500 ppm HVR solution is only 22.7 cP. However, the HVR solution has a relatively high viscosity remaining rate, which is approximately 58%. On the other hand, HVR solution has a good viscosity reducing ability on heavy oil. For the oil viscosities from 350 cP to 500 cP, the viscosity reduction rate of HVR at 2000 ppm is approximately 97% under the oil-water ratio of 3:7. In addition, the oil-water interfacial tension can be reduced by HVR solution at the concentration of 2500 ppm to 1.61 × 10−2 mN m−1. Comparing the asphaltene aggregates after interacting with HPAM and HVR, it illustrates that the layer spacing, interchain distance and diameter of the aromatic sheets are lager if interacting with HVR; meanwhile height of the aromatic clusters and effective number of aromatic sheets are smaller due to the reaction with HVR. In addition, if compared with the asphaltene treated by HPAM, with the increase of HVR concentration, the absorbance of asphaltene in toluene treated by HVR solution decreased significantly. Overall, this new hyperbranched copolymer shows potential for applications in heavy oil viscosity reduction.

Fabrication of methyl methacrylate-based polymer particles by miniemulsion and combined miniemulsion/emulsion polymerization using an atomization apparatus

The present study evaluated the fabrication of methyl methacrylate-based polymer nanoparticles by miniemulsion and combined miniemulsion/emulsion polymerization using an atomization apparatus with two-fluid nozzle. In both reactions, the effects of the operational conditions were investigated on the morphology and particle size distribution of polymer particles. After multivariate analysis, it was observed that the size of the poly(methyl methacrylate) particles is a function of gas pressure in the experiments stabillized by sodium lauryl sulfate (SLS), but this did not occur in reactions stabillized by inorganic and polymeric stabilizers. The use of inorganic stabilizer made possible the fabrication of polymer particles smaller than 300 nm. In combined miniemulsion/emulsion polymerization with SLS, high concentrations of surfactant (> 0.4% w/w) and intermittent monomer feeding enabled not only an increase of the solid concentrations, but also a reduction of particle size. In addition, styrene-methyl methacrylate nanoparticles were successfully obtained (< 30 nm), according to dynamic light scattering and transmission electron microscopic analyses.

Study of metal-amino acid [Cr(III)-Trp]2+ complex and ninhydrin reaction: role of gemini micellar solution on rate constant

In this article, the study of metal-amino acid complex and ninhydrin reaction was examined in gemini micellar solution using a UV-visible spectrophotometric measurement. The role of varying amounts of gemini micellar systems on rate constant of the study was investigated. Initially, rate constant (k ψ) enhances, below cmc and levelling-off areas are, then, noticed up to 400 × 10−5 mol dm−3. Later, gemini offers a third region of fast enhancement k ψ above 400 × 10−5 mol dm−3. Gemini surfactant series provided more efficient implications on the study than pure water and their monomeric traditional surfactant system. The values of rate constant, k ψ, were determined under a set of different experimental reaction situations with the help of a computer-based procedure. Such unfamiliar behaviour developed by gemini micellar solutions was treated by pseudo-phase model of micellar activity. An electrical conductometric measurement was employed to measure critical micellar concentration (cmc) of pure gemini micellar solutions and mixed systems. Several activation parameters were also determined by Eyring’s equation and different constants. Data obtained confirmed that lower values of activation enthalpy (ΔH #) with large negative activation entropy (ΔS #) were attained in gemini than aqueous. A plausible reaction mechanism of the study has been discussed and proposed.

Cationic Bola Form Metallosurfactants Based on Isothiouronium, Synthesis and Anti-Microbial Activity

Abstract Two series of well-defined dimeric metallo-bolaamphiphiles (bola surfactants) with the coordinated metal ions (Cu, Co, Zn) were prepared. These oligomeric surfactants consist of simple monomeric cationic surfactant fragments which are coupled via the hydrophilic ammonium chloride head groups by C6 and C12 spacer groups of different lengths. FTIR and 1HNMR identification techniques confirmed the obtained products. Measurements of surface tensions showed that the synthesized Bola amphiphiles have the desired, relatively low critical micelle formation concentrations (CMC). Bola amphiphiles with long spacer groups (C12) have a pronounced surface activity. The properties of these cationic surfactant oligomers in aqueous solution such as micellization and surface activity were discussed in relation to spacer group. In addition, the synthesized compounds were examined for their anti-microbial activity using the agar diffusion technique.

Effects of Surfactant Compounding on the Wettability Characteristics of Zhaozhuang Coal: Experiment and Molecular Simulation

Abstract It is important to study the mechanism of wettability of Zhaozhuang coal with surfactant compoundings in order to prevent dust disaster in the process of coal seam mining. By means of molecular simulation, the amounts of water absorbed by different systems, which are composed of monomer surfactant molecules and Zhaozhuang coal molecules or compounding surfactant molecules and Zhaozhuang coal molecules, were compared in this paper. The simulation results show that the system composed of 0.2% sodium dodecyl benzene sulfonate (SDBS) and 0.3% alcohol polyoxyethylene ether (AEO3) had the maximum water absorption amount of 479, which is significantly better than that of other compounding methods and of each monosurfactant system. Analysis results show that the interference of non-ionic surfactant can greatly reduce the electrostatic repulsion between ionic surfactants and make the adsorption sites on the Zhaozhuang coal molecule more compact. The experimental results show that the decreasing percentage of the contact angle of this type of compounding solution on Zhaozhuang coal was 83.74%, which is the best of the six compounding methods. It has a high degree of consistency with the simulation results, and the molecular simulation method applied in this paper shows that it is convenient and accurate. This research plays a guiding role in dustproof work in Zhaozhuang coal mining.

Efavirenz nanomicelles loaded vaginal film (EZ film) for preexposure prophylaxis (PrEP) of HIV

Preexposure prophylaxis (PrEP) using oral or vaginal microbicide is an emerging and effective strategy to prevent HIV transmission. Vaginal film is becoming more acceptable and a convenient dosage form compared to cream, gel and suppository. Extremely poor aqueous solubility of efavirenz (EFV) limits its use as vaginal microbicide. The aim of this study was to develop and evaluate a monomeric surfactant free, rapidly soluble vaginal film of EFV (EZ film). EZ film was prepared using a tetrafunctional block polymer (Tetronic 1107), carrageenan and polyvinyl alcohol (PVA) by solvent evaporation method. First, different solubilizers were screened for EFV solubility, in vitro cytotoxicity and cell membrane integrity assay on HeLa cells. Optimized film was characterized for solid state, mechanical strength, epithelial integrity, in vitro drug release in simulated vaginal fluid (SVF), simulated seminal fluid (SSF) and in vitro anti-HIV activity. Optimized EZ film showed a particle size of 48 ± 3.8 nm with PDI of 0.299. Differential scanning colorimetry (DSC) thermogram suggested the complete amorphization of EFV within the film. EZ film rapidly disintegrated (30 s) with complete release of EFV in SVF and SSF. The film was found to be non-toxic to HeLa cells and showed similar anti-HIV-1 activity as that of EFV in DMSO. EZ film did not show any significant change in the TEER value in HEC 1A cell line. Hence, the findings from the current study strongly suggest that the EZ film could be a cost-effective and convenient dosage form for PrEP of HIV.

Evaluation of a novel morpholine-typed Gemini surfactant as the collector for the reverse flotation separation of halite from carnallite ore

In froth flotation separation process, the collector molecular design has a crucial effect on potash processing to ensure sustainable production of potassium fertilizer (KCl) that is important to secure food supply in human society. Carnallite is an important source of KCl fertilizer production in industry. Reverse flotation has been used to separate halite (NaCl) impurities from carnallite (KCl·MgCl2·6H2O) for carnallite resources. However, progress in the carnallite resource reverse froth flotation has been constrained by the inherent limitation of traditional collector molecules with a single hydrophilic head and single hydrophobic chain per molecule. Herein, a novel morpholine-based Gemini molecule with double hydrophilic heads and hydrophobic chains, butanediyl-α, ω-bis (morpholino tetradecylammonium bromide) (BMTB) was synthesized and applied as the flotation collector in the reverse flotation separation for carnallite mineral. The better flotation performance of Gemini BMTB was achieved, compared to the traditional monomeric surfactant N-(n-Tetradecyl) morpholine (TDM). The bench-scale froth flotation separation results revealed that BMTB exhibited outstanding affinity and selectivity for NaCl crystals from carnallite at natural pH, resulting in less collector dosages – only 1/3 of TDM molecules. In contrast with traditional monomeric surfactant TDM (120 g/t), less amount of Gemini BMTB (40 g/t) – only one third of TDM molecules, was needed to obtain higher KCl recovery (KCl recovery raised by 4.69%). Meanwhile, the grade of NaCl with 40 g/t BMTB collector (2.19%) was lower than that with 120 g/t TDM collector (3.91%), and the grade of KCl with BMTB collector (22.59%) was higher than that with TDM collector (22.12%). Therefore, this work demonstrated the next-generation of flotation collector for the reverse froth flotation separation of the carnallite resources.

Corrigendum to “Investigation on the gelatin-surfactant interaction and physiochemical characteristics of the mixture” [Journal of Molecular Liquids, 224 (2016) 900–908/MOLLIQ_2015_362

Abstract The effect of gelatin, a denatured protein on the micellization of a series of polyoxyethylated hexadecyl ethers (BC-X) were investigated through several physicochemical techniques such as surface tensiometry, contact angle measurement, fluorimetry, cyclic voltametry, zeta potential measurement, dynamic light scattering studies. The critical micellar concentrations (cmc) of BC-X increased with increase in gelatin concentration in the mixture which was also corroborated by other techniques performed. This increase in cmc was attributed to the decrease of monomeric surfactant concentration as a result of the formation of gelatin-BC-X complex. The surface excess concentration, minimum area per molecule, and surface pressure at the cmc were estimated from surface tension data. The free energies of adsorption and micellization indicated the micellization and adsorption at air/water interface to be spontaneous phenomena. Micropolarity and the aggregation numbers of the mixed systems were determined using the fluorescence behaviour of pyrene. The slanting nature of curve of polarity parameters-surfactant concentration in conjunction with appearance of pyrene excimer peak at the lower BC-X concentrations supported the stepwise growth of the micelles through the formation of pre-micellar aggregates. The entwining of the protruded chains of the surfactants around the gelatin moiety through polar and hydrophobic interactions was endorsed to be the main reason behind the formation of small sized mixed micelles. The zeta potential studies envisaged the surface of both gelatin and BC-X to have negative electrostatic potential independently. The decrease in the zeta potential of the gelatin-surfactant mixtures was attributed to the removal of fraction of the negatively charged BC-X surface as a result of casing by the hydrophobic and neutral segments of gelatin.

Photophysical behavior of heme group: Unfolding of hemoglobin and myoglobin in the presence of Gemini surfactants of different molecular architectures

Fluorescence studies were performed to determine the photophysical behavior of heme group in the presence of cationic Gemini surfactants of different architectures. Both hemoglobin and myoglobin were used to understand the heme group interactions with Gemini surfactants under the influence of temperature variation and were compared with homologous monomeric surfactants. The results were also supplemented from the size and zeta potential measurements of both proteins. Gemini surfactants showed marked effect on the unfolding behavior of hemoglobin that mainly contributed by the stronger hydrophobic interactions of double hydrocarbon chains as well as methylene spacer in the head group region with the hydrophobic domains of hemoglobin. Myoglobin with single polypeptide chain did not show similar unfolding behavior in the presence of Gemini surfactants rather it was readily solubilized in the surfactant solution and that too in the presence of monomeric surfactants rather than Gemini surfactants. The results highlighted the mechanistic aspects by which water soluble globular proteins interact with amphiphilic molecules of different functionalities and thus, helped to predict the interactions of both hemoglobin and myoglobin with the complex biological molecules possessing similar functionalities.